The invention relates generally to sensing technologies and, more particularly, to fiber optic sensing packages and systems for multi-point temperature measurements for a gas turbine, for example.
Temperature sensing is essential for safe and efficient operation and control of many industrial processes. Industrial processes such as gas turbine, coal boiler operation, combustion, power generation, and gasification involve the measurement of high temperatures either for real-time industrial process monitoring or for control and optimization.
Gas temperature is one of the critical control parameters for gas turbine operation, and any improvement of accuracies of the temperature measurement can improve turbine efficiency. The temperature at the exhaust duct of the compressor/gas turbine approaches 600-1200 degrees Fahrenheit (° F.) with a very strong gas mass flow, and the direct combustor temperature measurement for control purposes is beyond capabilities of most temperature measurement equipment. In combustion control practice, an annular array of thermocouples is used to measure exhaust temperature to control fuel flow into the combustor. Whenever a fault temperature, either too cold or too hot, is detected, either the fuel flow rate adjustment or a premature shutdown of the gas turbine occurs. Such a combustion control method requires accurate annular exhaust temperature measurement. However, current exhaust temperature measurement using the annular array of thermocouples (TCs) provides only limited sensing points, and the sensing spatial resolution is about half a meter which can be larger than optimum. Accordingly, a control strategy of the gas turbine has an excessive margin, which results a lower power generation efficiency and lower diagnostic capabilities. However, it is difficult to increase the number and location of the existing TCs from the current method due to their bulky packaging and excessive electrical wiring needs.
Silicon dioxide based quartz fiber material melts at high temperatures such as, for example temperatures at about 2700° F., and thus silicon dioxide material based tetrahedral fiber Bragg grating (FBG) sensors are thought to be of great potential to be used for multi-point temperature measurement from harsh environments such as turbomachinery systems, combustors, generators, engines, and gasifiers. Further, FBG sensors comprise high quality reflectors constructed in optical quartz fibers that reflect particular wavelengths of light and transmit other wavelengths. FBG sensors are advantageous as having low mass, high sensitivity, multiplexing capabilities, multi-point distribution capabilities, multi-sensing functions, and electromagnetic interference immunity.
Monitoring gas turbine operation conditions requires not only thermal stabilized fiber Bragg grating sensors, but also a robust fiber sensor package. It would be useful to have a sensor package that is easily deployable inside the gas turbine for multi-point temperature measurement or any transient thermal dynamics measurement. The installed fiber sensor packages should survive the initial gas turbine startup and transient temperature ramping from ambient up to 1000-1200° F. Considering the exhaust gas that may include CO, CO2, Nox, H2O etc, a fiber sensor package should be hermetically sealed not only for a reliable temperature measurement but also for maintaining strong mechanical strength against vibration, thermal cycles, and stress corrosion induced mechanical fatigues.
However, deploying fiber sensors in any industrial power generation system definitely requires a proper fiber sensor package and the corresponding installation methods. Meanwhile, since each industrial system operation condition may vary in temperature, pressure, flow-rate, vibration, and corrosion, for example, the installation methods may differ from one industrial system to another industrial system. It is desirable to have an improved FBG sensor package, installation method, and an integrated sensing system that can survive different harsh environmental conditions.